TOPIC:

ID Code: F3-21
Purpose: Illustrate the difference between the surface tension in water and in alcohol.
Description: One jar contains sand with water. The bottle has been tamped so that the sand grains have become aligned with very small cracks between them. The surface tension of the water will not allow the water to flow into these very small volumes. When the jar is squeezed, the cracks open up sufficiently to allow the water to flow into them, thus causing the water in the tube to fall.

A second jar contains sand with alcohol. Because alcohol has a much smaller surface tension than water, the alcohol will flow into the small cracks between sand grains, filling the space. When the alcohol bottle is squeezed, the volume is already filled with sand and liquid, so the alcohol level in the tube must rise.

Availability: Available

When the bottle containing water and sand is squeezed, I've noticed that its behaviour is not quite as described here. When I squeeze the bottle, the water level initially rises slightly, and then falls to below its starting point.

Is this just due to the compression of the empty top portion of the bottle, above the sand line? Or Is some more subtle effect at work?